Abstract:

A need was identified for a set of basic design tools for Multi-Effect Distillation
(MED) plant evaporators. This led to an investigation into the different types of
evaporators as well as further research on horizontal falling film evaporators as used
in the MED process. It also included the theory on these types of evaporators. In
order not to duplicate existing design tools, an investigation was also performed on
some of the tools that are currently available.
The first set of tools that were developed were tools, programmed in EES
(Engineering Equation Solver), for the vacuum system and the evaporator. These
programs can be used to simulate different parameters (like different mass flows and
temperatures). That enables the correct selection of components for the vacuum
system and can be used to address sizing issues around the evaporator. It can also be
used to plan the layout of the plant.
The second of the design tools was developed by designing and building a flow
pattern test section. From the flow pattern test section a set of curves for the wetted
length under different conditions was obtained which can be used in order to design
the sieve tray. This set of curves was found to be accurate for municipal as well as
seawater and can be used in the design of the sieve tray of the evaporator.
Further development can be done by implementing the figures of the wetted length
into a simulation package like, for example, Flownex (a system CFD (Computational
Fluid Dynamics) code that enables users to perform detail design, analysis and
optimization of a wide range of thermal-fluid systems). The background gained from
the study done on the evaporator can also be implemented into such a package. This
could solve the problem of different design packages by creating a single design
package with all of the above mentioned options included.